This invention relates to improved oral compositions useful in caries prophylaxis containing a water-soluble complex of indium (III) and malic acid.
By the term "oral composition" as used herein is meant a product which in the ordinary course of usage is not intentionally ingested, but is retained in the oral cavity for a time sufficient to contact substantially all of the dental surfaces. Such products include, for example, dentifrices, mouthwashes, chewing gums, and dental prophylaxis pastes and topical solutions for application in the dental office. The oral compositions for caries prophylaxis herein contemplated do not require ingestion for anticaries effect.
The efficacy of fluoride in caries prophylaxis is well established, to the extent that the topical application of aqueous solutions of various water-soluble fluorides has become a routine procedure in many dental offices and clinics. Moreover, toothpaste compositions containing certain fluorides have recently been recognized as effective against caries by the American Dental Association.
It is known that certain metallic ions can have a significant effect on the anticariogenic efficacy of fluorides. For example, a body of scientific literature shows that the use of a source of stannous ions in conjunctions with fluoride gives a more effective anticariogenic product than is attained with fluoride alone [J. C. Muhler et al., J.A.D.A. 51, 665 (1955)]. More recently, relatively low concentrations of In(III) have been found to coact with fluorides to provide a high level of anticariogenic activity (U.S. Pat. 3,175,951, granted Mar. 30, 1965).
One of the problems which has developed in the formulation of stable oral compositions containing In(III) is the propensity of this metal to hydrolyze to form insoluble "indium hydroxide" and/or react with other constituents of the composition to form very stable complexes or highly insoluble compounds. The occurrence of any of the foregoing can render the In(III) non-reactive with dental enamel.
Similar problems have been faced in the formulation of oral products containing stannous tin, and various solutions have been posed. For example, Holliday et al., U.S. Pat. No. 3,105,798, granted Oct. 1, 1963, teach the use of aldonate complexes of stannous tin, such as stannous gluconate, to provide a water-soluble source of stannous tin in a stable and enamel-reactive form. Although such complexing anions are useful in conjunction with stannous tin, they do not provide an effective means for preventing hydrolysis of In(III).